Agricultural equipment frequently must operate on soft ground, often on ground with the plastic characteristics of muck. The lighter equipment, such as small tractors, can usually provide sufficient floatation by the use of large tires, but these are inadequate for the heavier machines. Large blueberry-picking machines are a good example of the problem. The ground they must operate on is typically soft, and the machines have to be large enough to straddle a fully developed blueberry bush. These machines usually have large drive wheels that are vertically movable under the action of hydraulic actuators to accommodate the picking mechanisms of the machines to bushes of various height.
The use of endless track systems to provide support and traction on soft ground has been well established. Providing this feature as an addition to a standard machine having drive wheels subject to a wide range of vertical movement has presented considerable design problems, as one end of the track mechanism moves with the drive wheels, and the other is mounted on the main frame. Resulting variations in the distances between the axes of rotation must be accommodated. The present invention is directed at providing a traction system that can be added to a standard machine with minor modifications and low cost.